Phil B,
I'm very sorry. (And just to get this out of the way pronto, YOU ARE NOT BEING "SOFT" OR "DAFT". I believe that in some ways animals teach us more about the true nature of love than other people can. There is less ego stuff getting in the way.)
I lost my precious little baby kitten Winnie, November 2nd of last year and I have not gotten over it. I doubt I ever will. I have spent time at
www.petloss.com on their forum and the people there are very helpful and kind. It might be a bit too maudlin for some sensibilities, but that's really a minor thing. It helps to communicate with others who have had similar experiences and who also are the kind of large-hearted special people who aren't afraid to admitt that they are grieving over the loss of a pet.
I believe that God holds and keeps all things and that nothing is ever realy lost, animals, people, and even material things. There is a great deal of support from the various organized religions concerning the deaths of people, but very little support or consolation concerning the deaths of animals. The exception would be India. At least I have found the very view I stated above in the Bhagavad Gita and in the commentary on it by Paramahansa Yogananda.
It makes sense to me. If we have souls, so do animals. And I have no doubt that there is a God and that we do have souls, so therefore I believe that animals have souls. And the soul by very definition is eternal.
My youngest cat Winnie was run over, which in many ways is, I would guess, easier than having to do the right thing and put a dying and suffering animal to sleep, but no matter how a pet dies, we are prone to feeling guilt and confusion. We all think about the "if only's" and might have beens and in order to regain some small measure of control, blame ourselves and second guess ourselves. You loved your wonderful cat; you would not do anything but the best for her. Do not blame yourself or second guess yourself. What was your lovely cat's name? She must have been very special for you to miss her so much.
Try to remember all the time you did have with her. I only had a few short months with Winnie, and while I do have two other cats, I dearly wish I had her back again. There is very little that I wouldn't give up to have her back, but she was never really mine to begin with. She was only given to my keeping from God, who has her again now.
I do believe this, but it doesn't make the pain any easier, just as knowing you did the right thing doesn't help much either.
I am truly sorry for the loss of your lovely, sweet, precious cat. She is lucky to have spent this time with you, I think, and vice versa.